1. Field of the Invention
This invention relates generally to a printer, and more particularly to a printer in which a recording paper sheet introduced from a sheet introducing opening is guided by sheet guiding means to a portion between a platen and a printing head and discharged from a sheet discharging opening after data has been printed on the paper sheet by the printing head.
2. Description of the Related Art
FIG. 4 is a schematic view of an independent printer unit of conventional type as mentioned above. This printer is capable of printing data on continuous paper having rows of pin holes formed on both side thereof, or on a paper sheet of a predetermined size.
A cylindrical platen 12 is rotatably mounted in a horizontal position in a central portion of an outer case 10 of the printer. On one side of the platen 12, a printing head 14 is mounted and is movable parallel to the platen 12 in a longitudinal direction thereof.
A region in an upper surface of the outer case 10, which corresponds to the platen 12 and the printing head 14, is constructed as a main upper cover 18. The main upper cover 18 is pivotable on an axis 16 which is remote from the platen 12 and the printing head 14. When the main upper cover 18 is raised, the platen 12 and the printing head 14 in the outer case 10 can be accessed from above.
First and second pinch roller groups 20 and 22 are positioned under the platen 12 so as to be spaced apart form each other in a radial direction of the plate 12, and in contact therewith.
An another region in the upper surface of the outer case 10, which is located on the opposite side of the platen 12 concerning to the printing head 14 and does not correspond to the platen 12 and the printing head 14, is constructed as a paper sheet introducing guide 24. The paper sheet introducing guide 24 is so inclined that the end portion thereof, which is adjacent to the platen 12, is directed toward a contact position between the platen 12 and the first pinch roller group 20. The end of the paper sheet introducing guide 24 and the outer periphery of the platen 12 define a paper sheet introducing opening 26.
As is clearly shown in FIG. 5, a paper sheet intermediate guide 28 is arranged under the outer periphery of the platen 12, and extends along the outer periphery of the platen 12 with it being slightly spaced apart from the platen between the second and the first pinch roller groups 22 and 20. The base end of the paper sheet intermediate guide 28 extends under the paper sheet introducing guide 24 to go away from the platen 12.
A paper sheet presser 30 is arranged between the printing head 14 and the proximal end of the paper sheet intermediate guide 28 so as to contact the outer periphery of the platen 12.
A paper sheet (not shown), which is slid down on the paper sheet introducing guide 24 into the paper sheet introducing opening 26 while the platen 12 is rotated in the clockwise direction in FIGS. 4 and 5, is pinched between the platen 12 and the first pinch roller group 20. As the platen 12 continues its rotation in this direction, the paper sheet is pinched between the platen 12 and the second pinch roller group 22, then pressed on the outer periphery of the platen 12 by the paper sheet presser 30, and thereafter passes through a very narrow space between the distal end of the printing head 14 (which is not moving) and the outer periphery of the platen 12.
If, after the leading end of the paper sheet reaches the printing head 14, an input device (not shown) supplies a printing order to the printer, the printing head 14 moves at a predetermined speed from one end to the other end of the platen 12 in the longitudinal direction thereof, and prints data on the paper sheet in accordance with the order. After the printing head 14 has reached at the other end, it returns to the above described one end. During this return, the platen 12 rotates clockwise by a predetermined angle at a given speed so as to move the paper sheet by a specified distance in a circumferential direction of the platen 12. After that, the above described printing of the printing head 14 on the paper sheet and the movement of the paper sheet by the given distance by the platen 12 are repeated until no further printing order is supplied.
A pin feed tractor 32 for supplying continuous paper having rows of pin holes on both sides thereof is arranged on the opposite side of the platen 12 concerning to the printing head 14 in the outer case 10.
The region of the upper surface of the outer case 10, which is located on the opposite side of the platen 12 concerning to the printing head 14 and has the paper sheet introducing guide 24, faces the pin feed tractor 32, and is constructed as a sub-upper cover 34. The sub-upper cover 34 is pivotable on an axis which is remote from the platen 12 and the printing head 14. When the sub-upper cover 34 is raised, the pin feed tractor 32 in the outer case 10 can be accessed from above. The sub-upper cover 34 has a continuous paper introducing opening 36 for permitting continuous paper to be supplied to the pin feed tractor 32.
A continuous paper guide 38 is arranged under the paper sheet intermediate guide 28 so as so extend along the guide 28 between an exit of the pin feed tractor 32 and the paper sheet presser 30. When continuous paper is supplied by the pin feed tractor 32, the first and second pinch roller groups 20 and 22 are detached from the platen 12, i.e., removed from a continuous-paper passage between the continuous paper guide 38 and the paper sheet intermediate guide 28.
The pin feed tractor 32 intermittently moves the continuous paper in association with intermittent rotation of the platen 12 during the printing operation by the printing head 14.
Paper sheet or continuous paper on which data have been recorded are discharged by the intermittent feeding operation of the platen 12 or the pin feed tractor 32 to the outside of the printer through a paper discharge opening 40 defined between the upper end of the outer periphery of the platen 12 and the main upper cover 18 of the outer case 10.
In the conventional printer as described above, if the platen 12 is rotated in the reverse direction to feed the paper sheet backward after the rear end of the paper sheet has been introduced into the paper sheet introducing opening 26, the rear end of the paper sheet is caught in the gap between the paper sheet intermediate guide 28 and the distal end of the paper sheet introducing guide 24 so that the paper sheet cannot be further transferred backward. As a result, the rear end portion of the paper sheet is jammed at the paper sheet introducing opening 26. Works for removing the jammed paper sheet from the paper sheet introducing opening 26 is cumbersome. In addition, the jammed paper sheet cannot be used thereafter, due to folds, etc.
Reverse feeding of a paper sheet is necessary to correct the print start position or print correct start position on the paper sheet or the posture of the paper sheet when the paper sheet is oblique on the platen.